The present invention relates to a semiconductor light-emitting device, e.g., a laser diode or light-emitting diode formed of II-VI group compound semiconductor, for example.
In order to record and/or reproduce an optical disk and a magneto-optical disk at high density with high resolution, there is an increasing demand for a green or blue semiconductor laser which can emit green or blue light of a short wavelength.
Japan Journal of Applied Physics Vol.31 (1992) pp. L340 to L342 described a semiconductor laser having a DH (double hetero) structure composed of a ZnSe active layer and a ZnMgSSe cladding layer can be photo-excited to oscillate at room temperature. An oscillation wavelength of the semiconductor laser having the ZnSe active layer was 475.0 nm.
Further, Japan Journal of Applied Physics Vol.33 (1994), pp. L938 to L940 described a semiconductor laser having a SCH (separate confinement heterostructure) composed of a ZnCdSe active layer, a ZnSSe guide layer and a ZnMgSSe cladding layer.
In the above-mentioned two semiconductor lasers, the active layers thereof are not doped.
In the II-VI group compound semiconductor light-emitting device composed of at least one kind of II-group elements, such as Zn, Hg, Cd, Mg or Be and one kind of VI-group elements, such as S, Se or Te, many non-radiative recombination centers exist on the active layer which is the light-emitting layer, thereby causing a current--light output characteristic and a current--voltage characteristic to be lowered. As a result, the semiconductor light-emitting device becomes unreliable.
As factors that act as the non-radiative recombination centers, there are enumerated dislocations such as a misfit dislocation or a threading dislocation, a stacking fault, a point defect and a cluster thereof, each of which has a dangling bond.
A degradation nucleus of the above semiconductor light-emitting device causes the non-radiative portion to be enhanced through a so-called non-radiative recombination enhanced defect motion (referred to hereinafter as NRREDM). There is then the problem that the operation characteristic is lowered. In particular, if the point defect exists with high density or the point defect forms a cluster, then the point defect tends to act as a degradation nucleus. Further, the point defect not only acts as the degradation nucleus but also moves due to NRREDM, i.e., assumes the degradation process. Therefore, the point defect plays a very important role in degradation of the semiconductor light-emitting device.
Of the aforesaid degradation nuclei, the dislocation such as misfit dislocation and threading dislocation and the stacking fault which are giant defects can be improved based on a substrate used, a substrate treatment, a semiconductor layer structure and a crystal growth condition, i.e., they are external causes. However, the point defect occurs based on the crystal growth condition or the like as an external cause but the point defect intrinsically exists in order to lower a free energy based on thermodynamics. These point defects are difficult to be reduced. At the same time, the deterioration caused by these point defects has to be suppressed.